Fats and oils are triacylglycerides, or triglycerides. They are called triacylglycerides because they are esters formed from the reaction of fatty acids with glycerol, a trihydroxy alcohol: ##STR1##
The distinction between a fat and an oil is arbitrary. At room temperature a fat is solid and an oil is liquid. Most triacylglycerides found in animals are fats, while those in plants tend to be oils.
Fats and oils, the most commonly occurring lipids, are a major source of dietary energy. Fats and oils are among the three major energy sources in the human diet (carbohydrates and proteins being the other two). However, fats and oils contain about twice as much energy per weight as carbohydrates or proteins.
Metabolically, ingested fats and oils are hydrolyzed into monoacylglycerides, diacylglycerides, fatty acids, and glycerol, all of which can be absorbed through the intestinal wall. The body then (1) utilizes these hydrolyzed or partially hydrolyzed fats as raw materials to synthesize its own fats, (2) converts the fatty acids to other compounds such as carbohydrates or cholesterol esters; or (3) converts the fatty acids to energy. The effects of dietary fats on cholesterol metabolism is of particular interest due to reports which link high levels of cholesterol in the blood (hypercholesterolemia) with arterial disease.
Low fat diets have long been known to be an effective means for lowering the serum-cholesterol level in humans, and, thereby lowering the risk of hypercholesterolemia (see Keys et al., Science 112, 79 (1950); Mellinkoff et al., Am. J. Med. Sci., 220,203 (1950); Groen et al., Voeding, 13, 556 (1952); Keys, Circulation, 5, 115 (1952); Key et al., Clin. Chem., 1, 34 (1955)).
In 1957, Keys, Anderson and Grande, The Lancet, 2:959-66, demonstrated that human serum-cholesterol levels were influenced by the quality of the fats rather than the quantity. It was demonstrated that the intake of saturated fatty acids containing 12 or more carbon atoms produced increased serum cholesterol levels in humans. Unsaturated fatty acids were found to lower serum cholesterol levels.
Grande, Anderson and Keys, Am. J. Clin. Nut., 23 (9), 11841193 (1970), disclosed that serum cholesterol and serum phospholipids levels are higher in men having diets rich in palm oil (C.sub.16:0) when compared to men having diets rich in stearic acid (C.sub.18:0).
Bonanome and Grundy, N. Eng. J. of Med., 318:1244-8 (1988), have recently suggested that stearic acid (C.sub.18:0) is as effective as oleic acid (C.sub.18:1) in lowering plasma cholesterol levels when either replaces palmitic acid in the diet.
Solid fat products, e.g. shortening and margarine, contain high levels of saturated fatty acids; typically C.sub.12:0, C.sub.14:0, C.sub.16:0 and C.sub.18:0. These saturated fatty acids are necessary to maintain the desired physical and functional characteristics of the solid fat product.
Many fat/oil-containing nonliquid food compositions used today, e.g. shortening, margarine, require specific blends of fats and oils to produce the desired characteristics. The fat constituent of these blended products is referred to as a hardstock fat or hardstock. The desired functional characteristics of hardstock fats in shortenings are:
melting point between 35.degree. C. to 70.degree. C.; PA1 capability to form a workable plastic composition when blended with the desired oils (mixture rheology); and PA1 provide a stable fat/oil matrix at room temperatures in the form of a specific crystalline structure.
The melting point and physical behavior of fats and oils are determined by the fatty acid composition of the triacylglyceride. Long chain saturated fatty acids form linear chains that can fit compactly together, resulting in high van der Waals attractions; therefore, triacylglycerides containing long chain saturated fatty acids are solid fats. The following saturated triacylglyceride can fit into a solid lattice and is, therefore, a solid (i.e. fat): ##STR2## Unsaturated fatty acids contain kinks or bends that prevent the formation of neat compact lattices, therefore, triacylglycerides containing unsaturated fatty acids are liquid fats (oils). The following unsaturated triacylglyceride cannot fit into a solid lattice and is, therefore, a liquid (i.e. oil): ##STR3##
High melting point triacylglycerides (MP.gtoreq.70.degree. C.) are undesirable as hardstock fats because they tend to be waxy. Low melting point triacylglycerides are also undesirable as hardstock fats because they tend to be oil-like.
Triacylglyceride fats made from saturated fatty acids with more than about 17 carbon atoms are relatively reduced in calories because the fatty acids are poorly absorbed by the body. Unfortunately, the high melting point of these fatty acids gives them a waxy, unpalatable taste. For example, tristearin and tribehenin are seldom used in foodstuffs because of their waxiness.
Triacylglycerides are unique compounds in that they exhibit multiple melting points. The multiple melting point behavior (polymorphism) is the result of triacylglycerides crystallizing into distinct crystalline structures. The .alpha. form is the lowest melting and least stable. This form transforms to the more stable and intermediate melting .beta.' form. In some triacylglycerides the .beta.' form is the most stable, but generally, the highest melting .beta. form is the most stable. In single-acid, triacylglycerides, the transformation order is .alpha..fwdarw..beta.'.fwdarw..beta.. Mixed acid triacylglycerides and triacylglyceride mixtures show a much more complicated polymorphic behavior with the existence of multiple .beta.' and .beta. forms depending upon the detailed triacylglyceride structures at hand.
Crystal stucture is also especially important to the properties of shortenings and specialty fats, e.g. cocoa butter. It is well known in the art that certain kinds of fat crystals, most notably the beta-prime (.beta.') crystals, have the capacity to form a rigidly interlocking structure when suspended in a liquid component if the crystals are present in sufficient amounts. This results in a mixture which does not separate and which has a good creaming ability.
It is, therefore, important that the solid glycerides of a shortening be of the proper crystal type. A shortening that crystallizes in the beta-phase form often tends to be waxy or grainy. While these characteristics are desirable in some instances, and shortenings have been formulated to have a beta-phase crystalline structure, the most acceptable commercial plastic shortenings have good creaming ability and retain their appearance, volume and performance characteristics under adverse storage conditions. In order to provide such shortenings it is necessary that the solid triacylglycerides crystallize and remain in the beta-prime crystalline form.
In general, the method of attaining the beta-prime form desired for plastic shortening is to add a suitable "beta-prime-tending" highly hydrogenated or saturated fat as the hardstock. Included in this category are such fats as hydrogenated tallow, cottonseed oil, palm oil, certain of the fish oils, and rapeseed oil. Since the beta crystalline phase of triacylglycerides is more thermodynamically stable than the beta-prime-phase, even highly beta-prime-tending hardstocks tend to undergo transformation into the beta-phase, especially under adverse storage conditions. Thus it is highly desirable in the formulation of a plastic shortening to provide a highly beta-prime-phase tending hardstock. U.S. Pat. No. 3,597,230, Colby et al., issued Aug. 3, 1971, discloses certain combinations of .beta.'-tending hardtocks which co-act in a manner to provide 2 plastic shortening having improved polymorphic stability of the .beta.' crystalline phase.
The following references further describe the polymorphic phase structure of edible fats: Chapman, Chemical Reviews, 62, #5, 433-56 (1962); Jackson and Lutton, J. Am. Chem. Soc., 72, 519-21 (1950); Jackson and Lutton, J. Am. Oil Chem. Soc., 27, 276 (1950); U.S. Pat. No. 3,129,102, Sanders, issued Apr. 14, 1964; U.S. Pat. No. 3,265,507, Japikse, issued Aug. 9, 1966; and U.S. Pat. No. 2,521,242, Mitchell, issued Sept. 5, 1950.
In order to provide the above mentioned desirable hardstock characteristics, typical vegetable oils and animal fats used in foods contain long chain fatty acids. Generally, these are predominantly 12 to 18 carbons long and contain zero to three double bonds. Some oils, such as rapeseed oil, contain fatty acids having 20 or 22 carbons or higher.
Several references disclose triacylglycerides containing medium chain and long chain fatty acids. For example, U.S. Pat. No. 3,353,964, Seiden, issued Nov. 21, 1967, discloses a margarine oil made from corandomized triacylglycerides containing saturated fatty acids having 6-14 carbon atoms and saturated fatty acids having 20-22 carbon atoms. The triacylglycerides, a corandomized blend of hydrogenated rapeseed oil with coconut and/or palm kernel oil, are high in lauric acid (C.sub.12:0).
U.S. Pat. No. 4,390,561, Blair et al., issued June 28, 1983, discloses margarine compositions containing triacylglycerides made from palmitic (C.sub.16:0) or stearic (C.sub.18:0), oleic (C.sub.18:1)), and linoleic acid (C.sub.18:2).
U.S. Pat. No. 4,526,793, Ingenbleek et al., issued July 2, 1985, discloses lipid compositions for oral external or parenteral nutrition which include gamma-linoleic acid containing triacyglycerides.
U.S. Pat. No. 4,590,087, Pronketal, issued May 20, 1986, discloses triacylglycerides containing palmitic (C.sub.16:0) and C.sub.18-24 fatty acids which have butter-like properties and a reduced tendency to develop graininess.
U.S. Pat. No. 4,607,052, Mendy et al., issued Aug. 19, 1986, discloses triacylglycerides of the formula: ##STR4## where R represents an acyl fragment of a polyunsaturated fatty acid containing 18 to 22 carbon atoms, the acyl fragment being capable of being oxidized, and wherein n represents an integer varying from 2 to 16. The triacylglycerides are used as nutritional supplements to provide a source of polyunsaturated fatty acids.
Japanese patent application (Kokai) No. 62-295,996, Shoji et al., published Dec. 23, 1987, discloses a method of preparing plastic fats with improved spreadability. These plastic fats are prepared by directed ester exchange a 10.degree. C.-25.degree. C. of a mixture containing 75-95% (wt) of a liquid vegetable oil (e.g. safflower oil or sunflower) and 5-25% (wt) of a behenic acid-containing fat (e.g. rapeseed oil and mustard oil.) Shoji et al. do not identify the specific triacylglyceride products of the disclosed method.
Japanese patent application (Kokai) No. 63-022,133, published Jan. 29, 1988, discloses fat/oil compositions for pie pastry which are comprised of C.sub.20:0 -C.sub.24:0 saturated fatty acids and C.sub.16 -C.sub.22 unsaturated fatty acids and triglycerides containing the radicals of the fatty acids. These compositions are characterized by their good extending and spreading properties.
The art suggests that excessive consumption of fats containing C.sub.12:0 -C.sub.16:0 saturated fatty acids leads to an increase in plasma cholesterol levels, resulting in an increase incidence of arterial disease. However, the art does not provide a means of reducing the levels of these fatty acids in a hardstock fat while retaining the desired hardstock characteristics (i.e. melting point, mixture rheology, and .beta.'-tending crystalline form).
It is the object of the present invention to provide a hardstock fat which (1) has little or no C.sub.12:0 -C.sub.16:0 saturated fatty acid acyl groups (2) has a melting point between 35.degree. C. to 70.degree. C., (3) is capable of forming a workable plastic composition when blended with the desired oils and (4) provides a stable fat/oil matrix at room temperatures in the form of a .beta.'-tending crystalline form. These hardstock fats are further characterized by their lack of waxy mouth feel and by their being relatively reduced in calories.
It is also an object of the present invention to provide food compositions containing the above mentioned hardstock.